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  1. #1
    Join Date
    Jun 2008
    St Louis MO

    Default Question about adding bathroom in basement. Drains

    My buddy wants me to help him put a bathroom in his basement. I consider myself pretty handy and up to the task. But I'm a little confused on how we should do it.

    He has a room that is pretty good sized already being used for storage and a laundry room. So, we know where it's going to go.

    I know where I'm going to get the water supply from, that's easy. My question is on the drain for the toilet. Is it safe to just drain it into the drain that's in the floor? Or do I need to bust up the floor and add a wye into the drain from the upstairs toilet? If that's the case, then the bathroom downstairs is dead in it's tracks.

    The upstairs toilet is on the other side of the house and if we put the downstairs toilet below it or even on the same wall, it will cut his basement in half.

    I thought about one of those toilets, but it would have to pump the waste up the wall, across the ceiling, then wye into the waste. That's about 35-40 feet. I'd hate for a pipe to break or leak.

  2. #2
    Join Date
    Jan 2009

    Default Re: Question about adding bathroom in basement. Drains

    I'm not sure what youre referring to the drain that's already there. If it's a main drain then you would have to bust the floor, add a 3" y (or 4X3y) to serve the 1/2 bath. Off the new 3" line pull a 3X2 y up a wall with the 2" serving as a wet vent for toilet and drain for sink. 2x1 1/2 ty for lav sink 2" continues up and ties into venting system or through roof. Sound complicated? It's involved and if you don't have a decent understanding of drains and vents leave it to a pro. Sani-flo may be a little easier because you dont have to break in the floor but venting is still required, in fact you'll have to vent the grinder and sink separately, then tie them in above 40". The waste line should be fine from breakage if primed, glued and supported correctly.

  3. #3
    Join Date
    Jun 2009
    Syracuse, NY

    Default Re: Question about adding bathroom in basement. Drains

    I am currently in the process of doing basicly the same thing that you are doing. You do need to break up the floor to see what the main line looks like. You will also need at least a 3 inch drain for the toilet. That could turn into the biggest problem if the line that you have there currently is only a 2 inch line and it doesn't turn back into a 3 or 4 inch untill the other side of the basement. BUT... if you get lucky it will be 4 inch under the floor, then you just need to add a wye to go off to the toilet. I was not lucky and had to bust up most of the floor then redo most of the old cast iron pipe that has deteriorated over the past 120 years. Good luck with your project.

  4. #4
    Join Date
    May 2008
    Pacific Northwet

    Default Re: Question about adding bathroom in basement. Drains

    If this bathroom will make for 4 or more toilets in the house, then the main drain going out to the septic or public sewer should be at least 4". I'm not sure if there's any grace in the codes for adding to existing systems.

    Now this can be a little confusing: it can be 3" so long as there are 3 or fewer toilets on that branch line. But wherever the total number of toilets feeding into the main line becomes 4, then it needs to bump up to 4". So if you have 3 toilets, you may have a 3" line down to where the fourth toilet connects in.

    Sewer lines should NEVER shrink as they go downhill. That is, you can't have a 3" branch line connecting to a 2" branch line downstream.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

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